Objective This study seeks to assess behavioural risk in people with HIV receiving antiretroviral (ARV) therapy in Thailand and Cambodia and to test a strategy to modify these behaviours and consequently reduce the rate of HIV transmission. Specific Aims 1. Measure beliefs and perceptions about ARV therapy, particularly as they relate to HIV transmission 2. Identify characteristics at an individual, family, community and contextual level that predict sexual and injecting risk behaviour and behaviour change in people with HIV infection taking ARV therapy, and which may be modifiable through a counselling intervention 3. Develop and test a counselling-based intervention to reduce the level of risk behaviour among people with HIV infection taking ARV therapy. METHODS The project will be conducted in two stages over five years. The first stage will collect data on beliefs and perceptions, risk behaviours and the factors that predict risk behaviour. Stage two will use these data to develop a risk reduction intervention and test it for long term effectiveness. EXPECTED OUTCOMES 1. Identification of an effective means of modifying high risk behaviours in people taking ARV therapy in a developing country setting. 2. Increased ability to provide appropriate psychosocial support to infected persons and affected communities. 3. Increased capacity to undertake future behavioural research in this environment.